Re: Are automatic coercions ever going away?

[Sean Conner <sean@...>]

It was thus said that the Great William Ahern once stated:
> On Fri, Aug 01, 2014 at 03:04:33PM -0500, Steven Degutis wrote:
> > On Fri, Aug 1, 2014 at 2:57 PM, Sean Conner <sean@conman.org> wrote:
> > >   One situation I hit in C was the following:
> > >
> > >         static int foobar___index(lua_State *L)
> > >         {
> > >           foobar__s *foo = luaL_checkudata(L,1,TYPE_FOO);
> > >
> > >           if (lua_isstring(L,2))
> > >             ...
> > >           else if (lua_isnumber(L,2))
> > >             ...
> > >         }
> > >
> > > Odd bugs until I actually read the description for lua_isstring():
> <snip>
> > Oh wow. That's actually pretty unsettling. I remember reading in PIL
> > (third edition) to be careful about this, and even seeing it a second
> > time is still a bit unsettling.
> > 
> 
> A number is a much stricter type than a string. For me it's natural to check
> for an integer first before a string. But I also religiously keep language
> documentation open on my desktop (for Lua, C, POSIX, etc).

  And I'm so used to non-coersion [6] that it never crossed my mind and
well, it lead to bugs.

> I'm not a C++ programmer, but there's a parallel with the ranking of
> implicit conversions when dealing with overloaded functions.
> 
> Because of Lua's metamethod devices it's important to always be in the habit
> of generating a loose hierarchy of types in your mind when implementing
> function overloading. Otherwise they go to waste. If implicit coercions
> didn't have significant value, neither would metamethods.

  I don't think that way.  I don't use metatables for tables, I use them for
userdata, and for all the userdata interfaces I've written, I've found one
that overrides something other than __call, __index, __newindex, __gc,
__tostring or __len [7], that's how rarely I do overloading. [8]

  I almost overrode __concat (or __add, I was dithering) for a protocol
handler I was writing, to add TLVs [9] to an outgoing packet, but I decided
against it at the last moment as "being too cute."

> Yes, often times you're trying to cram a square peg into a round hole. But
> it's darned convenient. It's up to the programmer to rank things so he tries
> fitting the round peg into the round hole first. Abstractions have costs
> because they necessarily obscure context. But that's their value!
> 
> I feel like the obsession with stricter typing is turning into an
> anti-pattern.

  I've checked the source control logs and over the past month, I've logged
50 bugs in a work related project written in Lua [1].  Four of the bugs are
work arounds to bugs in other components I have no control over; two were
reverted (found not to be a bug or the wrong fix for a bug); 31 were logic
or misunderstandings (in other words, a compiler would not have caught
these) and the remaining 13 were bugs that a compiler or stricter typing
would have caught. [3]

  -spc (Who likes his footnotes)

[1]	It processes SIP messages.  Man, is SIP an annoying protocol. [2]

[2]	Read:  I don't know the SIP protocol like the back of my hand and
	I really don't want to read 121 RFCs.

[3]	Now, one might reasonably ask why 13 typos got into the source
	control reposity.  I might answer as that's the only way to get the
	code to the target machine for interoperability testing [4].  This
	is also the first time I've seen actual SIP messages from the wild
	[5].

[4]	Seriously.  I need to run at least three other programs to even
	start testing this code.  

[5]	Equipment from other companies we need to interoperate with.

[6]	Assembly was my second language I learned; I've been using C for 25
	years now.  I've only been using Lua for a few years.

[7]	POSIX signal sets.  I defined __add, __sub and __umn methods.

	https://github.com/spc476/lua-conmanorg/blob/9be9c1145184aad515864c5a50ba6a7f64b4e418/src/signal-posix.c#L1147

[8]	For operators like '+' or '*'.  

[9]	Tag, Length, Value.  It's a popular format where I work.